In recent years, notebook-type personal computers have been used in increasing numbers, each having a PC card socket which accords with the standards of PCMCIA (Personal Computer Memory Card International Association), an American association, and with the standards of JEIDA. Various techniques have been developed to use this PC card as a video capture card or an MPEG decoder card, for controlling the input and output of motion-picture data.
System architecture having a PCI local bus is now used increasingly in order to process a great amount of data, such as motion-picture data, with high efficiency. This is because the PCI local bus can transfer data at high speed.
If the PCI local bus is used, however, its data-transferring ability is limited. The data-transferring ability of the PCI local bus is insufficient when the PC card is used as a video capture card or an MPEG decoder card as is mentioned above.
Recently, a technique has been developed. The technique is to connect a PC card and a display controller directly, by a so-called ZV (Zoomed Video) port, which is a bus designed exclusively for transferring motion-picture data. The ZV port enables the PC card to output video/audio data directly to the display controller/audio controller, without using the system bus. This solves the problem that the system bus is occupied for a long time to transfer a great amount of video data, thereby enhancing the video-data processing ability of the system.
Recently, multimedia techniques have advanced also in the field of personal computers. Various devices other than PC cards, which handle motion-picture data, are now incorporated in the system. These devices will be exemplified as follows:
(1) Video capture: Converting analog video signals from an imaging device such as a video camera to digital data, and inputting the digital data.
(2) MPEG decoder: Expanding motion-picture data compressed by MPEG, thus generating live motion-picture data.
(3) High-speed serial interface, e.g. IEEE1394: Inputting motion-picture data transferred from a digital video camera, a digital video player, and the like.
These devices are connected to the system bus in most cases. Therefore, the motion-picture data output from these devices will be transferred to the display controller through the system bus.
(1) Usually, the system bus has a bandwidth large enough to transfer motion-picture data. The rate of transferring motion-picture data must therefore be lowered in order to transfer motion-picture data through the system bus. If the transfer rate is lowered, the resolution of the motion picture will decrease, the frame rate thereof will decrease, or the number of bits per pixel will decrease. Consequently, the motion picture will be deteriorated in quality.
(2) The motion-picture data transfer mostly occupies the bandwidth of the system bus. The operations other than the motion-picture transfer via the system bus, for example the data transfer between the device and a disk drive will become slow. Further, the device may not normally operate, failing to transfer data in real-time fashion. If a communication device such as a modem does not operate normally, for example, a part of data may not be transmitted.